FIG. 17 shows the structure of a conventional automatic compensation sensor, in which reference numeral 1 is a sensor body. Reference numeral 2 is a microcomputer including an analog compensation signal output circuit, analog signal input circuit, memory circuit, and its peripheral circuits. Components such as a temperature sensor when the purpose of the automatic compensation sensor is to compensate for temperature are also included in reference numeral 2. Hereafter, reference numeral 2 including peripheral circuits is called a microcomputer 2. Reference numeral 3 is a signal adder to which the output of the sensor body 1 and the output of the microcomputer 2 are connected. Reference numeral 4 is a signal output circuit comprising an amplifier. Reference numeral 5 is a signal output terminal. The output signal of the signal adder 3 is connected to the analog input terminal 21 of the microcomputer 2. Reference numeral 6 is a compensation mode signal input terminal, and is connected to a digital input terminal 22 of the microcomputer 2. During compensation, an external signal source is connected to this compensation mode signal input terminal 6.
Operation of the above automatic compensation sensor is described below. The microcomputer 2 has two modes: a compensation mode and a normal operation mode. The compensation mode is activated when a compensation signal is input from the compensation mode signal input terminal 6. In other cases, the automatic compensation sensor operates in the normal operation mode.
One example of the compensation signal is a determination by high and low logic levels. The compensation mode signal input terminal 6 is pulled up inside the automatic compensation sensor by a resistance. If the compensation mode signal input terminal 6 is normally at "high" level when the compensation mode signal input terminal 6 is open, the microcomputer 2 is able to recognize the compensation mode by applying "low" voltage to the compensation mode signal input terminal 6. Accordingly, the microcomputer 2 is capable of determining the compensation mode by checking the voltage level of the digital input terminal 22.
Here, it is necessary to take appropriate measures to make it impossible to apply low voltage after compensation is completed, to prevent the compensation mode signal input terminal 6 from being erroneously set to the compensation mode.
Furthermore, if there is a possibility that the compensation mode signal input terminal 6 may be accidentally set to "low" by noise, the possibility of erroneous setting to the compensation mode may be reduced by configuring the compensation signal using serial communications.
This automatic compensation sensor requires an exclusive input terminal for the compensation mode signal used for sending compensation signals during manufacturing processes. This needs to be appropriately processed on completion of the automatic compensation sensor to prevent erroneous compensation operation of the sensor. If compensation can be tested during assembly, it may be relatively easy to modify the exclusive input terminal for the compensation mode signal. However, in case of angular velocity sensors, for example, correct output characteristics may not be obtained during assembly, requiring the adjustment of a finished product identical to those to be shipped. There are many such types of automatic compensation sensors. In this case, modifying the exclusive input terminal for the compensation mode signal becomes extremely difficult, complicating the terminal and case structure of the automatic compensation sensor and thus increasing the cost.